Control units which are used to control the distribution of electric current to a plurality of electric loads, such as a number of motors, from a central location, are generally housed in compartmented structures called control centers. Such control centers are formed of a group of individual control center sections each of which includes a plurality of cells or compartments wherein the control units are installed. Each control center section houses a number of control units vertically stacked one on top of the other. To facilitate wiring and servicing, control centers are provided with main horizontal bus bars which extend across the upper portions of all of the individual control center sections and which are connected to deliver current from a supply to groups of individual vertical bus bars in each control center section. Electrical current is supplied to the control center via the horizontal bus bars and is distributed through the vertical bus bars that run the length of each control center section. The vertical bus bars in turn deliver the current to the control units within the individual control center sections through separable jaw-like connectors which make contact with the vertical bus bars.
If a control unit were to be installed onto current carrying vertical bus bars while it was in the ON position, damage could be caused to the electrical distribution system, the control unit or the equipment which the control unit is controlling. Therefore, control units utilize an interlock mechanism to prevent them from being installed onto vertical bus bars when the control unit handle is in the ON position. Interlock mechanisms in the prior art require the user to manually engage the interlock mechanism when the control unit is fully engaged with the vertical bus bars. Therefore, there is a need to provide an interlock mechanism which automatically engages when the control unit is fully inserted into the control unit compartment.